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Astronomy 305/Frontiers in Astronomy

Astronomy 305/Frontiers in Astronomy. Class web site: http://glast.sonoma.edu/~lynnc/courses/a305 Office: Darwin 329A (707) 664-2655 Best way to reach me: lynnc@charmian.sonoma.edu. Group 12. Way to go, Group 12!. Golden Age of Cosmology. Standard Big Bang Cosmology

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Astronomy 305/Frontiers in Astronomy

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  1. Astronomy 305/Frontiers in Astronomy Class web site: http://glast.sonoma.edu/~lynnc/courses/a305 Office: Darwin 329A (707) 664-2655 Best way to reach me: lynnc@charmian.sonoma.edu Prof. Lynn Cominsky

  2. Group 12 Way to go, Group 12! Prof. Lynn Cominsky

  3. Golden Age of Cosmology • Standard Big Bang Cosmology • Big Bang Nucleosynthesis • Cosmic Microwave Background • Did the Universe have a bout of Inflation? • Horizon Problem • Flatness Problem • Multiverses • Geometry and Curvature of Space Prof. Lynn Cominsky

  4. Big Bang? Prof. Lynn Cominsky

  5. Big Bang Big Bang Timeline Big Bang Nucleosynthesis We are here Prof. Lynn Cominsky

  6. Standard Big Bang Cosmology • Sometime in the distant past there was nothing – space and time did not exist • Vacuum fluctuations created a singularity that was very hot and dense • The Universe expanded from this singularity • As it expanded, it cooled • Photons became quarks • Quarks became neutrons and protons • Neutrons and protons made atoms • Atoms clumped together to make stars and galaxies Prof. Lynn Cominsky

  7. Standard Big Bang Cosmology • Top three reasons to believe big bang cosmology • Big Bang Nucleosynthesis • Cosmic Microwave Background • Hubble Expansion Big Bang by Physics Chanteuse Lynda Williams Prof. Lynn Cominsky

  8. Big Bang Nucleosynthesis • Light elements (namely deuterium, helium, and lithium) were produced in the first few minutes of the Big Bang The predicted abundance of light elements heavier than hydrogen, as a function of the density of baryons in the universe (where 1 is critical) Note the steep dependence of deuterium on critical density. Goal is to find a critical density that explains all the abundances that are measured Prof. Lynn Cominsky

  9. Big Bang Nucleosynthesis • Heavier elements than 4He are produced in the stars and through supernovae • However, enough helium and deuterium cannot be produced in stars to match what is observed – in fact, stars destroy deuterium in their cores, which are too hot for deuterium to survive. • So all the deuterium we see must have been made around three minutes after the big bang, when T~109 K • BBN predicts that 25% of the matter in the Universe should be helium, and about 0.001% should be deterium, which is what we see. • BBN also predicts the correct amounts of 3He and 7Li Prof. Lynn Cominsky

  10. Big Bang Timeline Cosmic Microwave Background We are here Prof. Lynn Cominsky

  11. Cosmic Microwave Background • Discovered in 1965 by Arno Penzias and Robert Wilson who were working at Bell Labs • Clinched the hot big bang theory Excess noise in horned antennae was not due to pigeon dung! Prof. Lynn Cominsky

  12. Where is the CMBR? • Map of redshift vs. time after Big Bang Universe has expanded and cooled down by 1+z (about 1000) since the photons last scattered off the CMBR CMBR Z=1000 Prof. Lynn Cominsky

  13. CMBR • Photons in CMBR come from surface of last scattering – where they stop interacting with matter and travel freely through space • CMBR photons emanate from a cosmic photosphere – like the surface of the Sun – except that we inside it looking out • The cosmic photosphere has a temperature which characterizes the radiation that is emitted • It has cooled since it was formed by more than 1000 to 2.73 degrees K Prof. Lynn Cominsky

  14. Inflation Big Bang Timeline We are here Prof. Lynn Cominsky

  15. What is inflation? • Inflation refers to a class of cosmological models in which the Universe exponentially increased in size by about 1043 between about 10-35 and 10-32 s after the Big Bang (It has since expanded by another 1026) • Inflation is a modification of standard Big Bang cosmology • It was originated by Alan Guth in 1979 and since modified by Andreas Albrecht, Paul Steinhardt and Andre Linde (among others) Prof. Lynn Cominsky

  16. Alan Guth Why believe in inflation? • Inflation is a prediction of grand unified theories in particle physics that was applied to cosmology – it was not just invented to solve problems in cosmology • It provides the solution to two long standing problems with standard Big Bang theory • Horizon problem • Flatness problem Prof. Lynn Cominsky

  17. Horizon Problem • The Universe looks the same everywhere in the sky that we look, yet there has not been enough time since the Big Bang for light to travel between two points on opposite horizons • This remains true even if we extrapolate the traditional big bang expansion back to the very beginning • So, how did the opposite horizons turn out the same (e.g., the CMBR temperature)? Prof. Lynn Cominsky

  18. Horizon problem • The Universe at t = 300,000 y after the Big Bang (when the CMBR was formed) A and B are sources of photons that are now arriving on Earth Horizon distance is 1/100 of the distance between A and B Horizon distance is 3 x 300,000 y because the Universe is expanding – tells you how far light could travel Prof. Lynn Cominsky

  19. Horizon Problem • Inflation allows the early Universe to be small enough so that light can easily cross it at early times Prof. Lynn Cominsky

  20. No inflation • At t=10-35 s, the Universe expands from about 1 cm to what we see today • 1 cm is much larger than the horizon, which at that time was 3 x 10-25 cm Prof. Lynn Cominsky

  21. With inflation • Space expands from 3 x 10-25 cm to much bigger than the Universe we see today Prof. Lynn Cominsky

  22. CMBR vs. Inflation • Inflation also predicts a distinct spectrum of fluctuations for the CMBR which arise from the original quantum fluctuations in the pre-inflation bubble Everything we see in the Universe started out as a quantum fluctuation! Prof. Lynn Cominsky

  23. Flatness Problem • Why does the Universe today appear to have W between 0.1 and 1 – the critical dividing line between an open and closed Universe? • Density today will differ greatly from density of early Universe, due to expansion – if W starts out <1, it will get much lower and vice versa  only values of W very near 1 can persist • A value for W =1also implies the existence of dark matter as well as the cosmological constant Prof. Lynn Cominsky

  24. Flatness Problem • Density of early Universe must be correct to 1 part in 1060 in order to achieve the balance that we see Prof. Lynn Cominsky

  25. Flatness Problem • Inflation flattens out spacetime the same way that blowing up a balloon flattens the surface • Since the Universe is far bigger than we can see, the part of it that we can see looks flat Prof. Lynn Cominsky

  26. Uncertainty Principle DE Dt = h Big Bang Revisited • Extrapolating back in time, we conclude that the Universe must have begun as a singularity – a place where the laws of physics and even space and time break down • However, our theories of space and time break down before the singularity, at a time of 10-43 s, a length of 10-33 cm, and a density of 1094 cm3 • This is known as the Planck scale Prof. Lynn Cominsky

  27. Uncertainty Principle DE Dt = h/2 Uncertainty Principle Dx Dp = h/2 Planck scale activity • The goal of this activity is to calculate the Planck mass, length, time and energy. • Remember Prof. Lynn Cominsky

  28. Vacuum fluctuations • Virtual particle pairs continually emerge and disappear into the quantum vacuum • If you observe the particles, you give them enough energy to become real • The particles can also get energy from any nearby force field Prof. Lynn Cominsky

  29. Quantum Universe • Edward Tryon (1970) suggested that the Universe has a total E=0 because in a flat Universe, the negative energy of gravity is exactly balanced by the positive energy of matter • With E=0, there is no time limit on the Universe’s existence from the Uncertainty Principle • The quantum fluctuation Universe will collapse again due to the gravity of the singularity, unless it is given a sudden surge of energy • Spontaneous symmetry breaking of the previously unified forces provides this energy Prof. Lynn Cominsky

  30. Unified Forces • The 4 forces are all unified (and therefore symmetric) at the Planck scale energy inflation Planck scale Prof. Lynn Cominsky

  31. Symmetry Breaking • Here is an example: it is unclear which glass goes with which place setting until the first one is chosen Prof. Lynn Cominsky

  32. Broken Symmetry • At high T, the Universe is in a symmetrical state, with a unique point of minimum energy • As the Universe cools, there are many possible final states – but only one is chosen when the symmetry breaks Prof. Lynn Cominsky

  33. False Vacuum • The unified (symmetric) state of the very early Universe is a state of negative energy called the false vacuum • A phase transition turns the false vacuum into the true vacuum and provides the surge of energy that drives inflation – similar to the energy released when water freezes into ice • During inflation, spacetime itself expands faster than the speed of light Prof. Lynn Cominsky

  34. False Vacuum • The Universe is now stuck in a state of false vacuum which decays very slowly • When it reaches the true vacuum state, inflation will stop and particles will form The shallow slope near the false vacuum allows the Universe to keep the energy density almost constant as it expands Prof. Lynn Cominsky

  35. Pocket Universes • As the false vacuum decays, particles are created in “pocket universes” In each time slice, the original pocket universe expands by a factor of 3 while new ones are created out of the false vacuum in a fractal pattern Prof. Lynn Cominsky

  36. Formation of child Universe • As false vacuum expands, space distorts to form a wormhole Truevacuum Falsevacuum This entire region is 10-25 cm wormhole Prof. Lynn Cominsky

  37. True vacuum Child Universe False vacuum Child Universe • The child universe disconnects from the original space Observers in the parent universe see a black hole form! Prof. Lynn Cominsky

  38. Multiverses • Universe was originally defined to include everything • However, with inflation, the possibility exists that our “bubble universe” is only one of many such regions that could have formed • The other universes could have very different physical conditions as a result of different ways that the unified symmetry was broken • New universes may be forming with each gamma-ray burst that makes a black hole! Prof. Lynn Cominsky

  39. A Humbling Thought • Not only do we not occupy a preferred place in our Universe, we don’t occupy any preferred universe in the Multiverse! Prof. Lynn Cominsky

  40. Cosmological curvature parameters W = density of the universe / critical density • < 1hyperbolic geometry W = 1flat or Euclidean W > 1spherical geometry Prof. Lynn Cominsky

  41. Flatland by Edwin A. Abbott • The characters in Flatland: Rank in Flatland is a function of increasing symmetry: A woman, soldier, workman,merchant, professional man, gentleman, nobleman, high priest Prof. Lynn Cominsky

  42. Flatland • What do they see when a 3D being (Lord Sphere) comes to visit? 3D cross-sections of Lord Sphere float through the 2D world of Flatland Prof. Lynn Cominsky

  43. Troubles in Flatland • It’s hard to eat in a 2D world! • It is also impossible to tie your shoes! Why? A digestive tract cuts a 2D being in half! Prof. Lynn Cominsky

  44. Troubles in Flatland • A Square and his wife alone in their 2D house, when Lord Sphere drops in from the third dimension There is no privacy in 2D from a 3D being! Prof. Lynn Cominsky

  45. Troubles in Flatland • A 3D being would be able to change the symmetry of a 2D resident or help him escape from jail! The 3D being can lift the 2D resident up out of Flatland! Prof. Lynn Cominsky

  46. Troubles in Flatland • How do Flatlanders know the shape of their Universe? • A flat plane (with edges) is an open 2D Universe • Is there a closed 2D Universe? movie A Moebius strip is a 2D closed universe Prof. Lynn Cominsky

  47. Exploring Geometries • Take the newspaper • Cut a long skinny strip • Twist one end of the strip once and tape together • Congratulations – you have just made a Moebius strip! • How many sides does this have? Try drawing on it to see. • What happens to it when you cut it all around the strip direction? Prof. Lynn Cominsky

  48. Troubles in Flatland • What would happen if Flatlanders walked all the way around a closed 2D world? • They would be mirror-reversed! • Flat torus – another example of a closed 2D world Prof. Lynn Cominsky

  49. Infinite Universe? • Is the Universe infinite or just really, really, really big? • Some scientists (like Janna Levin) prefer to think of the Universe as finite but unbounded. An example of such a space is a 3D torus. • With such a topology, we could see the backs of our heads, if we could see far enough in one direction Prof. Lynn Cominsky

  50. Curved Space • This is not an infinite series of reflections, but is caused by light traveling all the way around the hyperdonut • A hyperdonut is one example of a curved space in 3D Prof. Lynn Cominsky

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